1. Field of the Invention
The present invention relates to an elastic wave resonator and also relates to a band pass filter and a duplexer including the elastic wave resonator.
2. Description of the Related Art
To date, elastic wave resonators have been used for band pass filters and duplexers of cellular phones.
The elastic wave resonators have reflectors arranged across at least one interdigital transducer (IDT) electrode in an elastic-wave propagation direction. An elastic wave resonator described in International Publication 2015/033891 includes two IDT electrodes arranged in a direction orthogonal to the elastic-wave propagation direction. Each IDT electrode shares a common busbar serving as a busbar of the corresponding IDT electrode. When the common busbar is shared, waves generated between the two IDT electrodes are coupled, and structural symmetry is thus improved. Nonlinear distortion can thus be reduced.
In recent years, an effort to obtain better filter characteristics has led to a larger size in an elastic-wave propagation direction of an IDT electrode of an elastic wave resonator and has also led to a longer busbar. Also in the elastic wave resonator described in International Publication No. 2015/033891, enhancement of the filter characteristics involves a longer common busbar. This increases line resistance, and insertion loss thus tends to be increased.